Thanks for the extra info, Key Biscayne for you if you want the beach and sand. You have a car so it's easy, besides taking a taxi from Key Biscayne to any where in the city is not very expensive. I'll bet you can get your $900.00 a month rental over there.
I would suggest Sunny Isles Beach or Aventura ,it's beautiful here, lots of places to keep you busy and entertained , ocean is minutes away and what's most important is Safety! You can jogg or walk at 4 am and feel safe! As to being close to nightlife of the southbeach scale it's never safe, anywhere where crazy parties all nights long to say the least.but believe me it's better to live in a safe place and take a cab to a party scene.
I will gladly help you in Sunny Isles or Aventura area if you choose to. Do your homework before you make a move! All the best,
Tatiana V Kolomiets 305.987.7470
305 705 9105
Visit my website: http://www.yolandecitro.com